I have created a custom image field to display the time remaining from 48h to 0h until an SLA expires :

IMAGE("/img/samples/color_green.gif", "", 12, max(0, 48 - Chrono_DureeCourante__c) ) &
IMAGE("/img/samples/color_white.gif", "", 12, 1 ) &
IMAGE("/img/samples/color_red.gif", "", 12, min(48, Chrono_DureeCourante__c) ) &
IMAGE("/s.gif", "", 12, 3 ) &
text(max(0, round((48 - Chrono_DureeCourante__c), 1))) &
"h"

Chrono_DureeCourante__c is a number between 0 and 48.

This is what the result looks like :

I have tried changing the way the text is displayed (second-last line) : no good.

Is this a bug ?   Is there a way of sorting correctly ?

Rup